docs: def register_decoder(self, lookup: Lookup, decoder: Decoder, label: str=None) -> None:
          """
          Registers the given ``decoder`` under the given ``lookup``.  A unique
          string label may be optionally provided that can be used to refer to
          the registration by name.  For more information about arguments, refer
          to :any:`register`.
          """
          self._register_coder(self._decoders, lookup, decoder, label=label)